This invention relates to an improvement in curved deflectors used for intercepting and collecting as a layer on the deflector liquid thrown as a relatively high velocity spray from a moving member.
In the pulp and paper industry there are numerous instances in which liquids are thrown off at high velocity from a moving member. For example, in pulping operations, dewatering devices involving centrifugal separation techniques to dewater a pulp suspension require the collection of large amounts of liquids. Similar occurrences of high velocity liquid sprays thrown from moving members occur in paper and paper-board forming and pressing equipment. In the forming section the breast rolls and wire rolls in a Fourdrinier web former throw off large quantities of liquid at high velocity, and deflectors are often used to intercept and direct the liquid into a receptacle or receptacles. In the press section, liquid is thrown from suction rolls and grooved rolls and is collected by various means. Common to all of the foregoing examples of liquid collecting devices in the pulp and paper industries, as well as to similar equipment in other industries, is the desire to collect the liquid in a vessel with a minimum of aeration of the liquid and to keep the noise created by impingement of high velocity showers or sprays against the elements of the liquid collecting equipment as low as possible.
The problem of collecting large amounts of liquid moving at very high velocity in a spray is particularly acute in high speed web-forming machines of the type described and shown in Webster U.S. Pat. No. 3,056,719. In such web-forming devices, a fibrous web is formed in a curved forming space defined between a foraminous or porous belt held under tension toward a curved support, which can be a solid or perforated roll or a solid or perforated shoe. A ribbon-like jet of stock is introduced to the forming space and is then subjected to dewatering by a combination of unit pressure developed by virtue of the tensioning of the foraminous belt toward the curved support and centrifugal force generated in the stock as it moves through the curve. Throughout the forming zone, liquid is thrown out through the foraminous belt at a velocity substantially equal to the velocity of the moving foraminous belt. The Webster patent type formers are capable of being operated in speeds in excess of 5,000 feet per minute, and there are now many commercial installations throughout the world in which such speeds are common.
The collection devices for capturing the high velocity spray of liquid thrown off the foraminous belt in the Webster patent type formers comprise a large collector vessel that is, in some present commercial installations, equipped with one or more curved deflectors spaced along the extent of the curved forming zone. The inner ends of the deflectors are located close to the foraminous belt, and each deflector extends generally transversely across the entire width of the forming zone and presents a concave surface facing the high velocity liquid spray being thrown from the foraminous belt. The deflectors serve at least two purposes: first, they collect the spray and turn it into a layer or sheet on the concave face of the deflector and in the process deaerate the liquid; second, they change the direction of flow of the liquid and guide it toward the lower portion of the collector vessel, from which it is conducted away.
A problem with collection devices of the type described above is that a very high velocity jet of liquid is discharged from the end of the deflector either against a wall of the vessel or into an accumulation of liquid in the bottom of the vessel. One or more perforated plates or screens can be interposed between the bottom of the vessel and the trailing or downstream end of the deflector to break up and slow the jet, but there is inevitably some high velocity flow-through of the jet directly into the residual liquid in the bottom of the vessel. Moreover, the jet impinges at high velocity against the perforated plate or screen and becomes aerated and makes a lot of noise in so doing. Both with and without devices for breaking up the high velocity jet flowing off the end of the deflector, there is, therefore, inherently a great tendency toward aeration of the liquid, which creates problems when the liquid is recycled, and generation of undesirable levels of noise.